Remove fmt::Display impls on Markdown structs

These impls prevent ergonomic use of the config (e.g., forcing us to use
RefCell) despite all usecases for these structs only using their Display
impls once.

src/librustdoc/externalfiles.rs

@@ -36,7 +36,7 @@ impl ExternalHtml {
                 load_external_files(md_before_content, diag)
                     .map(|m_bc| (ih,
                             format!("{}{}", bc, Markdown(&m_bc, &[], RefCell::new(id_map),
-                                    codes, edition, playground))))
+                                    codes, edition, playground).to_string())))
             )
             .and_then(|(ih, bc)|
                 load_external_files(after_content, diag)
@@ -46,7 +46,7 @@ impl ExternalHtml {
                 load_external_files(md_after_content, diag)
                     .map(|m_ac| (ih, bc,
                             format!("{}{}", ac, Markdown(&m_ac, &[], RefCell::new(id_map),
-                                    codes, edition, playground))))
+                                    codes, edition, playground).to_string())))
             )
             .map(|(ih, bc, ac)|
                 ExternalHtml {

src/librustdoc/html/markdown.rs

@@ -1,9 +1,6 @@
 //! Markdown formatting for rustdoc.
 //!
-//! This module implements markdown formatting through the pulldown-cmark
-//! rust-library. This module exposes all of the
-//! functionality through a unit struct, `Markdown`, which has an implementation
-//! of `fmt::Display`. Example usage:
+//! This module implements markdown formatting through the pulldown-cmark library.
 //!
 //! ```
 //! #![feature(rustc_private)]
@@ -16,8 +13,9 @@
 //!
 //! let s = "My *markdown* _text_";
 //! let mut id_map = IdMap::new();
-//! let html = format!("{}", Markdown(s, &[], RefCell::new(&mut id_map),
-//!                                   ErrorCodes::Yes, Edition::Edition2015, None));
+//! let md = Markdown(s, &[], RefCell::new(&mut id_map),
+//!                                   ErrorCodes::Yes, Edition::Edition2015, None);
+//! let html = md.to_string();
 //! // ... something using html
 //! ```
 
@@ -27,7 +25,7 @@ use rustc_data_structures::fx::FxHashMap;
 use std::cell::RefCell;
 use std::collections::VecDeque;
 use std::default::Default;
-use std::fmt::{self, Write};
+use std::fmt::Write;
 use std::borrow::Cow;
 use std::ops::Range;
 use std::str;
@@ -46,9 +44,8 @@ fn opts() -> Options {
     Options::ENABLE_TABLES | Options::ENABLE_FOOTNOTES
 }
 
-/// A tuple struct that has the `fmt::Display` trait implemented.
-/// When formatted, this struct will emit the HTML corresponding to the rendered
-/// version of the contained markdown string.
+/// When `to_string` is called, this struct will emit the HTML corresponding to
+/// the rendered version of the contained markdown string.
 pub struct Markdown<'a>(
     pub &'a str,
     /// A list of link replacements.
@@ -691,13 +688,13 @@ impl LangString {
     }
 }
 
-impl<'a> fmt::Display for Markdown<'a> {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let Markdown(md, links, ref ids, codes, edition, playground) = *self;
+impl Markdown<'_> {
+    pub fn to_string(self) -> String {
+        let Markdown(md, links, ids, codes, edition, playground) = self;
         let mut ids = ids.borrow_mut();
 
         // This is actually common enough to special-case
-        if md.is_empty() { return Ok(()) }
+        if md.is_empty() { return String::new(); }
         let replacer = |_: &str, s: &str| {
             if let Some(&(_, ref replace)) = links.into_iter().find(|link| &*link.0 == s) {
                 Some((replace.clone(), s.to_owned()))
@@ -716,13 +713,13 @@ impl<'a> fmt::Display for Markdown<'a> {
         let p = Footnotes::new(p);
         html::push_html(&mut s, p);
 
-        fmt.write_str(&s)
+        s
     }
 }
 
-impl<'a> fmt::Display for MarkdownWithToc<'a> {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let MarkdownWithToc(md, ref ids, codes, edition, playground) = *self;
+impl MarkdownWithToc<'_> {
+    pub fn to_string(self) -> String {
+        let MarkdownWithToc(md, ref ids, codes, edition, playground) = self;
         let mut ids = ids.borrow_mut();
 
         let p = Parser::new_ext(md, opts());
@@ -738,19 +735,17 @@ impl<'a> fmt::Display for MarkdownWithToc<'a> {
             html::push_html(&mut s, p);
         }
 
-        write!(fmt, "<nav id=\"TOC\">{}</nav>", toc.into_toc())?;
-
-        fmt.write_str(&s)
+        format!("<nav id=\"TOC\">{}</nav>{}", toc.into_toc(), s)
     }
 }
 
-impl<'a> fmt::Display for MarkdownHtml<'a> {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let MarkdownHtml(md, ref ids, codes, edition, playground) = *self;
+impl MarkdownHtml<'_> {
+    pub fn to_string(self) -> String {
+        let MarkdownHtml(md, ref ids, codes, edition, playground) = self;
         let mut ids = ids.borrow_mut();
 
         // This is actually common enough to special-case
-        if md.is_empty() { return Ok(()) }
+        if md.is_empty() { return String::new(); }
         let p = Parser::new_ext(md, opts());
 
         // Treat inline HTML as plain text.
@@ -766,15 +761,15 @@ impl<'a> fmt::Display for MarkdownHtml<'a> {
         let p = Footnotes::new(p);
         html::push_html(&mut s, p);
 
-        fmt.write_str(&s)
+        s
     }
 }
 
-impl<'a> fmt::Display for MarkdownSummaryLine<'a> {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let MarkdownSummaryLine(md, links) = *self;
+impl MarkdownSummaryLine<'_> {
+    pub fn to_string(self) -> String {
+        let MarkdownSummaryLine(md, links) = self;
         // This is actually common enough to special-case
-        if md.is_empty() { return Ok(()) }
+        if md.is_empty() { return String::new(); }
 
         let replacer = |_: &str, s: &str| {
             if let Some(&(_, ref replace)) = links.into_iter().find(|link| &*link.0 == s) {
@@ -790,7 +785,7 @@ impl<'a> fmt::Display for MarkdownSummaryLine<'a> {
 
         html::push_html(&mut s, LinkReplacer::new(SummaryLine::new(p), links));
 
-        fmt.write_str(&s)
+        s
     }
 }
 

src/librustdoc/html/render.rs

@@ -2596,7 +2596,7 @@ fn render_markdown(w: &mut fmt::Formatter<'_>,
            if is_hidden { " hidden" } else { "" },
            prefix,
            Markdown(md_text, &links, RefCell::new(&mut ids),
-           cx.codes, cx.edition, &cx.playground))
+           cx.codes, cx.edition, &cx.playground).to_string())
 }
 
 fn document_short(
@@ -2866,7 +2866,7 @@ fn item_module(w: &mut fmt::Formatter<'_>, cx: &Context,
                        </tr>",
                        name = *myitem.name.as_ref().unwrap(),
                        stab_tags = stability_tags(myitem),
-                       docs = MarkdownSummaryLine(doc_value, &myitem.links()),
+                       docs = MarkdownSummaryLine(doc_value, &myitem.links()).to_string(),
                        class = myitem.type_(),
                        add = add,
                        stab = stab.unwrap_or_else(|| String::new()),
@@ -2963,7 +2963,7 @@ fn short_stability(item: &clean::Item, cx: &Context) -> Vec<String> {
             let mut ids = cx.id_map.borrow_mut();
             let html = MarkdownHtml(
                 &note, RefCell::new(&mut ids), error_codes, cx.edition, &cx.playground);
-            message.push_str(&format!(": {}", html));
+            message.push_str(&format!(": {}", html.to_string()));
         }
         stability.push(format!("<div class='stab deprecated'>{}</div>", message));
     }
@@ -3017,7 +3017,7 @@ fn short_stability(item: &clean::Item, cx: &Context) -> Vec<String> {
                     error_codes,
                     cx.edition,
                     &cx.playground,
-                )
+                ).to_string()
             );
         }
 
@@ -4248,7 +4248,7 @@ fn render_impl(w: &mut fmt::Formatter<'_>, cx: &Context, i: &Impl, link: AssocIt
             let mut ids = cx.id_map.borrow_mut();
             write!(w, "<div class='docblock'>{}</div>",
                    Markdown(&*dox, &i.impl_item.links(), RefCell::new(&mut ids),
-                            cx.codes, cx.edition, &cx.playground))?;
+                            cx.codes, cx.edition, &cx.playground).to_string())?;
         }
     }
 

src/tools/error_index_generator/main.rs

@@ -101,7 +101,7 @@ impl Formatter for HTMLFormatter {
                 };
                 write!(output, "{}",
                     Markdown(desc, &[], RefCell::new(&mut id_map),
-                             ErrorCodes::Yes, DEFAULT_EDITION, &Some(playground)))?
+                             ErrorCodes::Yes, DEFAULT_EDITION, &Some(playground)).to_string())?
             },
             None => write!(output, "<p>No description.</p>\n")?,
         }